Glycan chains are major components of cells and extracellular molecules, with a complexity rivalling that of nucleic acids and proteins. This program continues to focus on two major types of anionic glycans at the outermost aspects of the cell surface glycocalyx - Sialic Acids (Sias) and the Glycosaminoglycan (GAG) chains Hyaluronan (HA), Heparan sulfate (HS) and Chondrotin suflate/Dermatan sulfate (CS/DS). The structures of sialylated N- and O-glycans of blood cell and plasma glycoproteins are well described. Specific glycan-binding proteins differentially recognize these Sias, including CD33-related Siglecs (l-type lectins with cytosolic signaling motifs, on specific blood cell types) (Project 2). Some beta-galactoside-specific lectins detect the selective absence of certain Sias on proteins involved in hemostasis and immune function, affecting their regulation and turnover (Project 1). The GAG chains of HS and CS/DS proteoglycans regulate multiple processes in endothelial biology, including angiogenesis and leukocyte migration (Project 3). Fragments of HA generated by specific hyaluronidases can also ligate pattern detection receptors such as TLRs (Project 4). Most physiologic and pathological roles of Sias and GAGs are not evident in cultured cells, but must be explored in the intact organism - and this complexity of mammalian glycans is not well represented in model invertebrates. Thus, the central theme of this proposal is state-of-the-art genetic manipulation of Sias, GAG chains, and some of their cognate binding proteins in the mouse. When systemic gene inactivation models are non-viable or have confusing phenotypes, we will selectively inactivate mouse. genes in a cell type-specific and developmentally-regulated manner. In some instances, transgenic overexpression of genes is appropriate to answer specific questions. This approach allows a specific focus on glycans and glycan-binding proteins of blood cells, endothelium, and plasma proteins. Over the past 10 years, we have assembled and sustained a highly interactive team of experts to analyze the consequences of such genetic manipulations on the structure and function of hemostatic, immune and vascular systems, focusing on functional consequences on plasma protein turnover, angiogenesis, and the leukocyte-mediated immune responses. Many more opportunities for intellectual and practical collaborations and synergies have also emerged. These studies will reveal many important functions for glycans in health and disease.